Machines for dry ice cleaning make use of mixing devices, into which dry ice granulate and pressurized gaseous medium, usually compressed air, are supplied separately in order to create a stream of dry ice.
This technical solution relates to devices, which comprise fixed housing wherein rotating feeding element is placed. In such devices, rotating element is in the form of rotating feeding disk, or in the form of rotating feeding roller. Devices comprising the rotating feeding disk as rotating feeding element are described e.g. in documents NL 1015216 C2, WO 8600833, U.S. Pat. No. 6,346,035 and EP 1 637 282 A1. Devices comprising the rotating feeding roller as rotating feeding element are described e.g. in documents U.S. Pat. No. 4,974,592 and CN 2801303.
The device serves for mechanical transport of dry ice granulate into a system with the flow of gaseous medium (air), whereas mixing of dry ice with the flow of air and creation of dry ice stream occur, mainly for cleaning purposes. Both the systems, i.e. the inlet of dry ice stored in a container and the inlet of compressed air, have different pressure. It is important to maintain tightness of the air system, for correct function and efficiency of the device. Mechanical transport of dry ice granulate is carried out by rotating feeding element, which comprises transporting cavities. Cavities filed with granulate from the container are moved by rotation of the feeding element to the system with the flow of air, and granulate is then carried by this flow of air away, whereby transporting cavities are discharged. Remaining pressure from the air system, left in the cavity after its discharge and before refilling the cavity, is equalized through pressure release channels to ambient pressure.
As it was mentioned above, it is important to maintain tightness of the air system for correct function and efficiency of the device. In the case of devices with feeding disk, the tightness is obtained by forcing the fixed plates against the rotating feeding disk, either directly, see NL1015216, or through sealing elements, see EP 1 637 282 A1, WO 8600833 and U.S. Pat. No. 6,364,035 B1. In the case of devices with the feeding roller, the tightness is obtained by forcing of shaped sealing elements against the rotating feeding roller.
With regard to high pressure in the air system, to provide sufficient tightness for devices with the feeding disk, high manufacturing precision of the main parts of the device, fixed plates and the rotating disk, and also relatively great force for holding fixed plates against the rotating feeding disk, is necessary. This results in fast wearing of relevant friction parts, whereas regular tightness check and tightness adjustment by tightening of fixed plates against the feeding disk is necessary during device operation, what increases operational costs. When relevant parts of the device are worn-out their replacement is then necessary, what basically means replacement of fixed plates and the feeding disk as the main and the most expensive parts of the device. This disadvantage is obvious with device type as described in document NL1015216 C2.
To overcome the disadvantage of wearing-off of the main parts of the device, as mentioned above, solutions were proposed for sealing, which make use of sealing elements placed between the fixed plate and the feeding disk, as described in EP 1 637 282, WO 8600833 and U.S. Pat. No. 6,364,035.
Mentioned solutions provide for that fixed plates do not have to be manufactured with high precision, as it is required for direct contact of the fixed plate and the feeding disk, and when worn-out it is sufficient to replace worn-out sealing elements only.
When using dry ice cleaning machine, it is not always necessary to have the air system work under full working pressure, and therefore, with lower working pressures smaller forces for holding fixed plates against the feeding plate are sufficient for sealing the pressurized part. However, with solutions described in NL1015216 C2 and EP 1 637 282 A1, force exerted by fixed plates is constant and to ensure the tightness, this force is still equal to a force necessary for sealing the highest pressure in the air system, although such a force of fixed plates is not needed. Though in the case of the solution according to EP 1 637 282 A1, worn-out parts replacement costs are not high, the disadvantage of the need to check the tightness and to adjust it by tightening of fixed plates against the feeding disk still stays. This disadvantage is also present with the solutions having rotating feeding roller, where force exerted by shaped sealing elements against the feeding roller must be checked.
Mentioned operational disadvantage present with devices having the feeding disk, is eliminated by solutions according to WO 8600833 and U.S. Pat. No. 6,364,035 B1, where a pressure let to the air system regulates also the amount of force exerted upon the feeding disk, either through sealing elements, when mutual distance of fixed plates is constant, WO 8600833, or through fixed plates, when mutual distance of fixed plates varies, U.S. Pat. No. 6,364,035. Both described devices, although solving the problem of continuous adjustment of the force exerted against the feeding disk as a function of the pressure in the air system, however are complicated in design, what presents higher demands for the maintenance and reparation of such devices and also increase of their production costs.
In the case of solutions U.S. Pat. No. 4,947,592 and CN 2801303 with the feeding roller, exertion of force is realized by mechanical means, springs and adjusting cams.
Aim of the present invention is a device for mixing solid particles of dry ice with the flow of gaseous medium, which eliminates mentioned disadvantages of currently known devices.